In the early 18th century Pontypridd, then known as Pont-y-tŷ-pridd (The bridge of the earthen house),[5] was a tiny hamlet.[6] Pont-y-tŷ-pridd took its name from the original bridge of the same name,[6] however very little is known of that ancient ford with stepping stones, which ran alongside the current Old Bridge,[7] and was used only when the river ran low.[7] Possibly in 1744 or after the bridge was built,[7] Pont-y-tŷ-pridd became known as Newbridge or New Bridge after the William Edwards' Bridge.[7][8] By 1856, Newbridge had been renamed Pontypridd.[9]

In 1746 when William Edwards was just 27 years of age,[10] he was commissioned by the Hundreds of Miskin and Caerphilly to build a three-arch bridge across the River Taff.[11] For this he was paid the sum of GB£500, on condition that he would maintain it for seven years.[2][11]

The first bridge to be constructed was a three-arch stone bridge, which was built in 1746. It was destroyed by a heavy storm which caused the River Taff to flood about two years later.[12] A large amount of debris came down the river, which then become trapped against the two abutments supporting the bridge.[1] The weight and force of the debris ultimately destroyed the bridge, which was then swept away down the river.[1]

After the destruction of the first bridge over the fast flowing River Taff, William Edwards decided to design a much more radical 140 ft (43 m) single-arch bridge that would eliminate the possibility of debris destroying the bridge due to the flooding of the River Taff.[1] The second bridge was built from 1748, however two reports differ as to what actually happened during this second attempt to build the bridge. Thomas Morgan, contemporary of Edwards, said that "…when he (William Edwards) had almost finished the arch; the centre timber work gave way and all fell to the bottom." However, The National Library of Wales have a contemporary works known as the Plasybrain manuscript which says that, "Just after the first single arch was finished and before the centre was struck, a flood came and carried all away." It is not clear which one of these two accounts is the accurate one, however it is clear that Edwards' latest attempted to build a bridge cross the River Taff had yet again ended in failure.[1]

The single-arch bridge was rebuilt and was actually finished. It stood for a period of about six weeks before again it collapsed because the new bridge was not balanced, which forced the keystone out, which once again caused the bridge to collapse.[1] In the Theory of Arches and Pontypridd, it states that "the weight of the bridge was either too great on the haunches or too little on the crown."[10] At this stage Edwards was either encouraged or forced to try again with extra money being provided to cover his losses for the earlier attempts.[10]

The final design of the bridge included three cylindrical voids (holes) of 2.7 m (8.9 ft), 1.7 m (5.6 ft) and 1.1 m (3.6 ft) on each side on the bridge.[11] This reduced the weight and pressure on the crown and the bridge is still in operation today, however it can only be used by pedestrians. The Theory of Arches and Pontypridd, states that as a bridge, the bridge was a failure, as it was "only eleven feet wide between the parapets and so steep that wagons had to use a 'chain and drag' to descend from the crown."[1]

The 140 ft Old Bridge surpassed the 130 ft (40 m) Old Walton Bridge as the longest single span bridge in Great Britain and remained the longest bridge for another 40 years.[10][13] It was also one of the few bridges in Europe, and indeed worldwide, whose span exceeded the 40 m mark.

The whole project (including the three failed attempts) cost the architect a total of £1,153 18s. 2d. (approximately £1,153.91), and consequently he made a loss of over £600.[6] It was reported that Edwards' attempts to build the bridge over the River Taff left him in a considerable amount of debt and Thomas Morgan reported that "…the mason was considerably in debt and greatly discouraged. But the Lords Talbot and Windsor, who have estates in the neighbourhood pitied his case, and being willing to encourage such an enterprising genius, most generously promoted a subscription among the gentry in those parts."[1]

The problem with the Old Bridge was that it was so steep that it made it very difficult to get horse carts to go across it.[14] By 1857, a new bridge, the Victoria Bridge, was built next to the Old Bridge, which was paid for by the people of Pontypridd.[14] The Victoria Bridge is a three-arch bridge, that was built by Thomas Jenkins, this overcame many of the problems with the steepness of the Old Bridge.[15]

Representations of William Edwards' Bridge can be seen in local heraldic and civic stationery, including the crest of Pontypridd Rugby Football Club, and Cilfynydd Rugby Football Club.[19] The community-to-community organisation PONT (Partnerships Overseas Networking Trust), also bases its logo upon the Bridge.[20] Pontypridd High School in Cilfynydd incorporates the bridge design into the school shield,[21] as does Pontypridd Town Council with its logo representing the south Wales Valleys and a section of the Old Bridge in the foreground.[19]Pontypridd Male Voice Choir also incorporates the Old Bridge in the choir logo.[22]